Quick-Start TCP

Quick-Start TCP was codified in an Experimental RFC (RFC 4782) in 2007. Based on explicit feedback from the network, it can use a large Initial Window, with the goal to speed up the initial phase of transfers over underutilized paths. The approach was later extended to DCCP in RFC 5634.

The protocol roughly works as follows: The sender asks the network for its desired sending rate, by putting an IP option in its first packet (containing the SYN TCP segment) to a receiver. Routers on the path can then accept the request, refuse it, or accept it with a reduced rate. The resulting rate is then echoed back by the receiver. The protocol must detect the case where there are Quick-Start-agnostic routers in the path. Since it requires explicit router support that current routers don't have, it is not likely to be seen used in the Internet today.